In the manufacture of semiconductor devices such as LSIs and ULSIs, or liquid crystal display panels, and such, light is applied to a semiconductor wafer or a liquid crystal original panel to form a pattern; when dust is adhered to an exposure original plate (photolithography mask) used here, the dust absorbs or bends light, and thus the transferred pattern is deformed, the edge is made rough and the base is stained black, with the result that dimensions, quality, appearance and the like are disadvantageously degraded.
For this reason, these operations are generally performed in a clean room. However, since it is difficult to keep the exposure original plate clean all the time even within the clean room, a method of attaching a pellicle serving as a dustproof protection to the surface of the exposure original plate, which is obtained by adhering, to a pellicle frame, a pellicle film that highly transmits exposure light, is employed. In this case, dust is not directly adhered to the surface of the exposure original plate and is adhered to the pellicle film, and thus focusing on a pattern on the exposure original plate at the time of photolithography prevents the dust on the pellicle film from affecting the transfer.
A pellicle is basically configured as follows: a transparent pellicle film that is composed of materials highly transmitting exposure light such as nitrocellulose, cellulose acetate, fluorine polymer and other components is adhered by air drying to the upper portion of a pellicle frame composed of an aluminum alloy, such as A7075, A6061 or A5052, that is black alumite treated, a stainless steel, polyethylene and other components, to which a good solvent for a pellicle film is applied (see patent document 1), or is adhered with an adhesive such as an acrylic resin, an epoxy resin or a fluorine resin (see patent documents 2 and 3); furthermore, in order for the exposure original plate to be fitted to the bottom portion of the pellicle frame, an adhesion layer is provided that is composed of a polybutene resin, a polyvinyl acetate resin, an acrylic resin, a silicone resin or other resins; and a reticle adhesive protective liner for the purpose of protecting the pressure-sensitive adhesion layer is provided.
When the pellicle is adhered to the exposure original plate, a closed space is formed inside the pellicle. In this case, the pellicle film does not have air permeability, and thus the gas within the closed space expands and contracts as the temperature varies, with the result that the pellicle film swells upward or hangs downward. To prevent this, a pellicle is known in which air vents are formed in a pellicle frame (see patent document 4). As shown in FIG. 8, patent document 4 discloses a pellicle that is provided with: pellicle frame sides 12 in which air vents 11 are formed; and pellicle frame sides 13 applied an adhesive 14 which collects dust existing, entering and occurring in the closed space of the pellicle.
There is also an example of a pellicle in which no adhesive is used therewithin and air vents 11 are formed in a pellicle frame 12 with a filter 15 (see FIG. 9).
However, a pellicle that simply includes one or a plurality of air vents has poor ventilation efficiency, and, unless significant variations in air pressure within the closed space of the pellicle, for example, significant variations in air pressure under mask environments resulting from exposure, are produced, desired ventilation is not performed. When, in a photolithography process, ultraviolet rays (an i-line or a g-line, a KrF, laser beam, an ArF laser beam, a F2 laser beam or the like) are applied, exposure is performed or a photomask is stored, an organic or inorganic gas generated from the constituent components of the pellicle is released from the constituent components of the pellicle, is formed as a gaseous substance and is left within the closed space formed by the pellicle and the photomask; the gas photochemically reacts with ammonia or a cyanogen compound or other hydrocarbon compounds present in the environment under application of ultraviolet rays at the time of exposure to form a fog called a haze such as ammonium sulfate or fine particles; and it is difficult for the above-mentioned pellicle to cope with this situations.
Citation List
Patent Documents
[Patent document 1] JP-A-S58-219023
[Patent document 2] U.S. Pat. No. 4,86,1402
[Patent document 3] JP-B-S63-27707
[Patent document 4] JP-A-H3-166545
A pellicle is arranged so as to cover a pattern region formed on the surface of a mask substrate. Since the pellicle is provided to prevent the adherence of dust onto the mask substrate, the pattern region is isolated from the outer portion of the pellicle such that the dust on the outer portion of the pellicle is not adhered to the surface of the pattern.
In recent years, the design rule of LSIs has become finer into a sub-quarter micrometer order, and the wavelength of an exposure light source has become narrower accordingly, and specifically, the wavelength changes from a g-line (436 nm) and an i-line (365 nm) by a mercury lamp, which are conventionally used, to a KrF excimer laser beam (248 nm), an ArF excimer laser beam (193 nm), a F2 laser beam (157 nm) and the like. As the wavelength of exposure light becomes narrower as described above, the exposure light naturally has higher energy. When high-energy light is used, as compared with the light of conventional wavelength, it is highly likely that gaseous substances existing in an exposure atmosphere react to produce reactive products on the mask substrate.
To overcome this problem, attempts have been made to minimize gaseous substances within a clean room, to clean a reticle more carefully, to remove gas-generating substances from the constituent components of the pellicle and to take other measures. Since the pellicle, in particular, is used by being directly attached to a mask substrate, it has been required to reduce the production of gas from the constituent materials of the pellicle, namely, a reticle adhesive, a pellicle film adhesive, an inner wall coating agent or the like formed of organic material, and improvements have been made. However, the production of a fog-like foreign material called a haze on the mask substrate is not completely prevented even when the reticle is cleaned and the production of gas from the constituent materials of the pellicle is reduced, with the result that it is responsible for reduced yields in the manufacture of semiconductor.